Geology
The Pasig River's main watershed is concentrated in the plains between Manila Bay and Laguna de Bay. The watershed of the Marikina River tributary mostly occupies the Marikina Valley, which was formed by the Marikina Fault Line. The Manggahan Floodway is an artificially constructed waterway that aims to reduce the flooding in the Marikina Valley during the rainy season, by bringing excess water to the Laguna de Bay.
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